1. Field of the Invention
The present invention is directed to a process of forming arc tubes. More particularly, the present invention is directed to lamps having ceramic arc tubes exhibiting an increased lumen efficiency of 3-10% over conventional lamps with sintered arc tubes and the process of forming same.
2. Discussion of the Art
There is a great need for conservation of electrical energy by producing efficient lamps for the lighting industry. Hundreds of millions of lamps are sold each year, and a 3-10% improvement in lamp efficiency would result in higher quality products with considerable savings in electrical energy. Typically, lamp efficiency is defined by the lumen output of a given wattage lamp or by the normalized value of lumens per watt (LPW).
Currently, ceramic metal halide (CMH) lamps with high quality, white light are commercially available. CMH lamps are generally constructed with a ceramic arc tube made from a polycrystalline, translucent aluminum oxide. The optical quality of the ceramic arc tube in a CMH lamp partly determines the lumen efficiency of the lamp. For example, CMH 70 W lamps made with conventional or xe2x80x9cas-sinteredxe2x80x9d ceramic arc tubes typically exhibit relatively low LPW values of less than 85. Ceramic arc tubes employed in CMH 70 W lamps are initially prepared by sintering the ceramic arc tubes in a hydrogen furnace at temperatures near 1850xc2x0 C.
Still another problem with CMH lamp manufacture is the variation in light output from lamp to lamp. That is, it is always desirable that lamp manufacture result in a repeatable, consistently performing lamp. Thus it is important to control the standard deviation of lamp so that quality control in the manufacturing process is improved.
It would be advantageous to develop an improved lamp and method for making the above lamps that would increase lamp efficiency and improve the standard deviation or uniformity of light output from lamp to lamp.
In an exemplary embodiment of the present invention, a process for making an arc tube comprises the steps of sintering an arc tube composition to form the arc tube, and annealing the arc tube in a vacuum. Preferably, the arc tube annealed according to the present process is a ceramic arc tube. The annealing of the arc tubes in a vacuum preferably occurs at a temperature of between about 1000xc2x0 C. and 1500xc2x0 C.
In another exemplary embodiment, a process for making a ceramic metal halide lamp is provided. The process for making a ceramic metal halide lamp comprises the annealing process of the arc tube and additional steps to form the ceramic metal halide lamp.